Spatial constraints underlying the retinal mosaics of two types of horizontal cells in cat and macaque

TL;DR

This study investigates the spatial organization of horizontal cells in cat and macaque retinas, proposing that simple spatial constraints, rather than heterotypic interactions, explain the regularity of their mosaics.

Contribution

The paper introduces a computer model demonstrating that spatial constraints alone can account for the regularity of horizontal cell mosaics in retina.

Findings

High regularity index explained by spatial constraints

Heterotypic interactions are not necessary for mosaic formation

Model applies to both cat and macaque horizontal cells

Abstract

Most types of retinal neurons are spatially positioned in non-random patterns, termed retinal mosaics. Several developmental mechanisms are thought to be important in the formation of these mosaics. Most evidence to date suggests that homotypic constraints within a type of neuron are dominant, and that heterotypic interactions between different types of neuron are rare. In an analysis of macaque H1 and H2 horizontal cell mosaics, W\"assle et al. (2000) suggested that the high regularity index of the combined H1 and H2 mosaic might be caused by heterotypic interactions during development. Here we use computer modelling to suggest that the high regularity index of the combined H1 and H2 mosaic is a by-product of the basic constraint that two neurons cannot occupy the same space. The spatial arrangement of type A and type B horizontal cells in cat retina also follow this same principle.